Method and apparatus for sound transmission and reproduction



J. KALSEY Oct. 25, 1938.

METHOD AND APPARATUS FOR SOUND TRANSMISSION AND REPRODUCTION 2Sheets-Sheet 1 Filed Sept. 29, 1936 INVENTOR.

BY 7x iaae orwund.

ATTORNEY J. KALSEY Oct. 25, 1938.

2,134,047 METHOD, AND APPARATUS FOR SOUND TRANSMISSION AND REPRODUCTIONFiled Sept. 29, 1956 2 Sheets-Sheet 2 INVENTOR. Wm M 642a (S W.

ATTORNEY Patented Oct. 25, 1938 UNITED STATES PATENT OFFICE I METHOD ANDAPPARATUS FOR SOUND 15 Claims.

This invention relates to an improved method and apparatus forconverting acoustical energy into fluctuating impulses in an electriccircuit and, conversely, to convert fluctuating electric impulses intoacoustic energy; apparatus of this character being known as transmittersor microphones and also as telephone receivers and loud speakers.

As far as present knowledge extends, the only practical way to changeacoustical energy into fluctuations in an electric circuit by mechanicalmeans is to subject a diaphragm or other object to the vibrations ofsound waves, said diaphragm being capable of vibrating more or less inunison with the vibrations of the sounding body. This diaphragm, byvarious means, may change the resistance in an electric circuit, orgenerate electrical impulses, or do both.

The transformation of these electrical impulses into sound waves isbrought about by the magnetic flux variations produced by theseimpulses, said flux variations producing sound vibrations in suitableresponsive bodies.

From a physical standpoint, sound waves in air are very intricate to andfro motions of the gas molecules of which the air is composed, it mightbe assumed for the present purpose that the vibrations of the soundingbody transmit these vibrations to layers of air and each air layer thusset into vibration transfers its energy to adjacent layers. The actualdistance traveled by these individual layers is very minute.

In order to reproduce sound with absolute fidelity, the vibratingbodyemitting the reproduced sound must be able to copy all the motionsof the transmitting body or diaphragm and this diaphragm must be capableof responding to all of the pressure characteristics imposed upon it bythe original sound waves. Thus the motion or the ratio of the motion ofthis diaphragm must conform to the motion of the sound waves impingingupon it.

But the inertia of a conventionally suspended 45 diaphragm does notre-act upon the substance of which this diaphragm is composed in thesame way as the inertia of the gaseous bodies of which sound waves arecomposed act upon themselves and hence a conventional diaphragm can not50 truly conform to the motions of the sound waves. It is a known factthat all bodies set in motion will tend to vibrate according to theirphysical characteristics commonly called natural frequency. Thus adiaphragm, unrestrained from 55 vibrating with a natural frequency willbe unable to synchronize its motions with the motions of the soundwaves, hence causing distortion throughout the process of reproduction.

To minimize the effects of inertia and natural periods of inflection inpractically all cases the diaphragm has been solidly clamped along itsperiphery and in some instances has been tightly stretched or damped byvarious means.

This procedure, though it reduces uncontrolled vibration, makes thediaphragm less responsive to the complex sound vibrations acting upon itand further prevents equal response to the variations in frequencies,with the result that some of the sounds are liable to become over orunder emphasized and when such sounds are amplified will tend to greatlydistort the final reproduction.

Another factor, one perhaps not very well known, in the case of aflexible diaphragm, where movement is prevented at its periphery, anymotion of that portion within the periphery will produce molecularfriction within the substance of the diaphragm. This friction producessecondary sound waves, totally unlike the original sound waves, andthese secondary sound Waves again set up unrelated motions in thediaphragm which produce distortion.

Another factor, (perhaps of less importance but neverthelesscontributing to final distortion) is that a conventional diaphragm hasvarying degrees of flexibility at various points within its peripheryand sound Waves originating from various sources are apt to impinge uponvarious points of the diaphragm, which due to this varying degree offlexibility, can not respond with equal intensity.

In microphones where the diaphragm applies direct pressure uponelectro-resistive or generative material, for the purpose of producing afluctuating E. M. F., the phenomena is still further complicated, as theability of the diaphragm to respond to sound waves is also governed bythe ability of the resistive or generative material to assist or impedethe free motion of the diaphragm. 5

Most of the remarks about microphones may be applied to telephonereceivers and speakers.

Summarizing the objections to a conventional diaphragm, such as used intelephone apparatus, they are as follows: 4

l. Inertia action of the diaphragm is present;

2. Natural frequency vibrations in the diaphragm itself are alsopresent;

3. The diaphragm bends or flexes, which is objectionable as it producesmolecular friction within the material of the diaphragm and thisfriction produces sound entirely foreign to the sound waves actuatingthe diaphragm; also, due to the varying degrees of flexibility betweenthe center and periphery of the diaphragm it can not respond with equalintensity throughout its surface;

4. A conventional diaphragm must be clamped, stretched or damped topartially overcome some of the above mentioned defects;

5. A conventional diaphragm is not sufficiently sensitive and responsiveto complex sound vibrations to permit fidelity of sound transmission orlike production;

6. The conventional diaphragm is also hampered in its action,particularly in transmitters, by the pressure required to be exerted byit on the electro-resistive or generative material cooperatingtherewith.

The object of the present invention is generally to improve and simplifythe construction and operation of telephone apparatus of the characterdescribed; to provide a method and apparatus whereby the heretoforelisted defects are substantially overcome; and, further, and morespecifically stated, the object of the invention is to mount a diaphragmin a magnetic field of sufficient strength to oppose inertia forces andnatural periods of vibrations in the diaphragm and, in addition thereto,to providea floating mounting which will maintain the diaphragm parallelto the lines of magnetic flux in the magnetic field and secure thediaphragm against movement longitudinally of said lines but permitmovement transverse thereof; and, further, to provide means whereby twospaced diaphragms may be mounted in common or separated magnetic fieldsand whereby movement may be magnetically transmitted from one diaphragmto the other in any ratio desired.

The invention is shown by way of illustration in the accompanyingdrawings, in which- Fig. l is a diagrammatic view showing two magneticpoles of opposite polarity, said poles Fig. 3 is asimilar view showingthe insertion of two thin iron discs between the poles, said viewfurther showing how the lines of fiux are Fig. 4 is a diagrammatic viewof two poles of opposite polarity in which the lines of flux areconcentrated by projections E-E formed on the opposing faces of thepoles and also by the insertion of thin iron discs between theprojections;

Fig. 5 is a diagrammatic view showing how it is possible to furtherconcentrate the magnetic field;

Fig. 6 is a diagrammatic view showing a magnetic field of lessconcentration than that disclosed in Fig. 5;

Fig. 7 is a vertical, central section showing one method of suspending athin iron disc diaphragm in a magnetic field, said view further showingthe diaphragm connected with a voice coil;

Fig. 8 is a perspective view showing' the arrangement of permanentmagnets and two of the poles energized thereby;

Fig. 9 is a front view of Fig. '7;

Fig. 10 is a central, vertical section showing the arrangement oftwo'diaphragms in a magnetic field and one of said diaphragms beingconnected with a dust box; a

Fig. 11 is a central, vertical section showing a condenser type oftelephoneapparatus;

Fig. 12 is a perspective view showing the arrangement of the permanentmagnets and the poles energized thereby, said arrangement being employedin the structure shown in Figs. 10 and 11;

Fig. 13 is a central, vertical section showing another type of telephoneapparatus; and Fig. 14 is a perspective showing the arrangement of thepermanent magnets and the polepiece energized thereby as employed in thestructure of Fig. 13.

Extensive experiments with magnetic circuits have convinced me that afield of force existing betweentwo opposingmagnetic poles of equalstrength, having equal areas parallel to each other, consists ofparallel lines of energy, provided the field is not influenced byexternal forces. I have also determined that the lines wholly within thearea bounded by the magnets poles are neutral with respect to each otherbut capable of exerting a force upon the magnetic lines located outsidethis field.

Fig. 1 shows two such poles where the lines A are parallel and the linesB and C are curved.

It can be shown that the lines in area B and C are weaker than the linesin area A, and further that the forces exerted by the lines B and C areproportionate to the degree of their curvature and to the forcesdeveloped in area A.

Referring to Fig. 2. If a magnetic object, such as a thin iron disc isplaced within the field A, the lines within same will be distorted; anumber of these lines will function through the substance of which thedisc is composed and the number of lines thus affected will depend uponthe number of sympathetic atomic structures within the disc as comparedto the number of like structures within the magnet itself.

Provided these atomic structures within the disc are so proportioned asto be negligibly affected by the forces of gravitation as compared tothe forces exerted by the magnet, practically all of the inertia forcesinherent in these structures are subordinated to the forces within saidfield.

Inasmuch as magnetic forces are not affected by inertia, such astructure, if placed within the concentrated field designated as A, willbe devoid of motion in the absence of external motivating forces. Whenmotivating pressures are applied, the resulting motion will onlycontinue as long as this pressure maintains.

Again referring to Fig. 2, it can be experimentally demonstrated that ifthe aforesaid structure is placed within the field A as shown, and aforce is applied in the direction depicted by the arrow, and such forceis just sufficient to cause motion of the structure, this same force, ifcontinued, will move the structure to the position at a, and when thisforce is removed, the structure will remain at a. To continue moving thestructure beyond th point a would require a steadily increasing forceand after the removal of this force, either gradu-. ally or suddenly,the structure will return to the discs or diaphragms are placed thereinthe lines of flux tend to divide and concentrate about the individualdiscs. At the same time due to the flux action of the magnetic field, asecondary magnetic fiux is induced in the respective diaphragms causingmagnetic poles to form in the diaphragms themselves. The opposing polesformed will be alike and a repulsive action is thereby set up betweenthe diaphragms tending to separate them. This is of considerableimportance as it is due to this repulsive or separating action thatmotion transmitted to one diaphragm by the impact of sound waves willtransmit motion to a second diaphragm, as will hereinafter be more fullydescribed.

I have also discovered that division of the magnetic field is furtherpromoted by providing the magnets with annular projections, such asshown at E-E in Fig. 4, and that these fields may be narrowed, as shownin Fig. 5, or widened, as shown in Fig. 6. This is also of considerableimportance as it provides means for restricting motion of the diaphragmsin a direction transverse, or at right angles, to the lines of fiux.When the field is narrow, as shown in Fig. 5, it restricts the movementof the diaphragm and, conversely, if the field is widened, as shown inFig. 6, the diaphragm may be given a greater freedom or latitude oftransverse movement. In addition to the .above features, it may bestated that when the magnetic field is comparatively narrow, as shown inFigs. and 6, and particularly Fig. 5, the diaphragm will tend to assumea position centrally of the field and if pressure is exerted to move itout of the field in a direction transverse to the lines of fiux it willreturn to the center of the field the moment the activating force isremoved.

Again, as previously pointed out, where the field is wide, as forinstance in Fig. 1, the lines of flux are parallel and are substantiallyneutral with relation to each other and in that case the diaphragm maybe positioned within the field at substantially any point desired andwill remain in the position in which it is placed but when the diaphragmis moved toward the outer edges of the field it is effected by the linesindicated at B and C and movement out of the field is then resisted.

By proper application of the fundamentals pointed out in connection withthe Figs. 1 to 6, it is possible to oppose inertia forces in a diaphragmand the natural periods of vibration in the diaphragm. It is,furthermore, possible to employ a comparatively rigid diaphragm whichdoes not depend upon flexing action, but instead will move as a wholewhen impacted by sound waves. Again, it is possible to restrict movementof the diaphragm, or to permit greater latitude of movement than hasheretofore been possible, this phenomena being important where twodiaphragms are employed as motion can be magnetically transmitted fromone diaphragm to another at substantially any ratio desired.

Fig. 13 illustrates a practical application of the phenomena orprinciples just explained. The structure disclosed is a telephonetransmitter. It consists of a plurality of segmental shaped magnets,indicated at I, 2, 3 and I, which are separated with relation to eachother but positioned to form a ring. The magnetic sections are energizedfrom a pair of permanent magnets 5 and 6, or the like, so disposed thateach pole of each magnet contacts one segment of the ring and they arefurther disposed to causelthe north and south poles formed in thesegments to oppose each other, as shown in Fig. 8, so that the foursegments of the ring become four magnetic poles separated by four wideand equally spaced air gaps.

The magnetic field formed in the circular space between the segments isdivided into'two concentrated fields by the formation of annularprojections 1 and 8 on the inner faces of the segments and these fieldsare further concentrated by placing circular disc-like magneticdiapnragms, such as shown at i and 8 in the respective fields. Thediaphragms tend to assume a position centrally of each field, that is,midway of the width of the respective fields but are, nevertheless,freely movable laterally thereof, or within the width or" the field, therange of movement being determined by increasing or decreasing the widthof the fields. A circular disc placed in a field of this character,which is surrounded by magnetic poles and with a small air gap betweenits peripheral edge and the poles, would naturally tend to move radiallytowards one pole or another, unless held absolutely centrally positionedbetween the same, means must accordingly be provided to prevent radialmovement and said means must at the same time permit lateral movement ofthe diaphragm with relation to the respective magnetic fields. This isaccomplished by securing a' ring Ill to the peripheral edge of eachdiaphragm and similar rings II to the opposite faces of the segments andthen securing to said rings retainer rings l2, composed of thin fabricpaper or similar material. The retainer ring is best shown in Fig. 9. Itis cut out, as indicated at M, to form a series of arms l5. These armssecure the diaphragm against radial movement with relation to themagnetic poles but at the same time permit free movement laterallythereof. The diaphragm 8" is preferably enclosed by a housing l6constructed of non-magnetic material and this housing is evacuated topermit free movement of the diaphragm. Within this housing is mounted avariable resistance element, generally indicated at ll, of the typedisclosed in my copending application entitled Variable resistance filedJ an-' uary 4, 1936, Serial Number 57,541. This resistance ismagnetically actuated. It consists of a pair of electrodes spaced apartwith a paramagnetic material between them. The electrodes are connectedwith a source of current supply through wires I 8 and I9. When thepara-magnetic material is subjected to the flux action of a magneticfield it forms a conductor between the electrodes and permits a currentflow and as the flux strength increases, the conductivity increases andconsequently the current flow increases; vice versa, as the fluxstrength decreases conductivity decreases and current fiow decreases,hence by moving the diaphragm 8 toward or away from the variableresistance element the current flow therethrough will fluctuate andmovements of the diaphragm caused by sound wave impact will,accordingly, be converted into electrical impulses and these may, inturn, be converted into sound.

In actual operation the sound waves will impact the diaphragm indicatedat l and it will, 7

accordingly, move back and forth in its magnetic field in substantialunison with the sound waves. This movement will, in turn, bemagnetically transmittedto the second diaphragm 8 due to the repulsiveaction maintained between the same and also to the fiux action of themain field, and

the movement of the diaphragm 8 will, in turn, actuate the variableresistance and thereby electric fluctuations will be produced. Aspreviously stated, the range of movement of the diaphragm 8 withrelation to the diaphragm I may be substantially the same or it may bedecreased. For instance, by widening the magnetic field in which thediaphragm 1 is placed substantially any movement desired may bemaintained. On the other hand, by narrowing the magnetic field in whichthe diaphragm 8 is disposed the movement thereof will be decreased butit will be relative to the movement of the diaphragm 1 A ratio ofmovement between the two diaphragms is not absolutely essential with thetype of structure shown in Fig. 4 but it is essential when used inconnection with a conventional variable resistance or commonly calleddust box such as illustrated in Fig. 10. .Where a variable resistance ofthat characteris employed the movement of the diaphragm will be hamperedas the.

diaphragm is directly connected with the dust box through means of apiston, such as shown at 2|. That is, when movement is applied to the Iis shown. In this instance a single diaphragm diaphragm it istransmitted to the dust box through means of the piston. This applies adirect pressure upon the electro-resistive or generative materialcontained therein and as the material compresses it obviously affords aresistance to the movement of the diaphragm, hence in installations ofthis character the employment of two diaphragms is advisable as theouter diaphragm may in that instance be freely movable while the innerdiaphragm, which is connected with the dust box, may have acomparatively small movement, the movement being, however, in directratio to the movement of the outer diaphragm. Where the relativemovement is reduced, as in this instance, the resistive action of thedust box does not hamper the movement of the diaphragm to a detrimentalextent and fidelity of transmission results.

In the structure disclosed in Fig. 10 annular projections, such as shownat 1 and 8 (see Fig. 13), are not required as the pole segments are madein pairs, as shown at I-i 2-2 3-43 and 4-, with the legs of thepermanent magnets 5 and 6 disposed between them as clearly shown in Fig.12. In Fig. 13 the pole pieces i, 2, 3 and t are single, hence thenecessity for the annular projections I and 8 where a division of themagnetic field is desired. The permanent magnets employed in connectionwith the structure shown in Fig. 13 are secured to the segments, asshown in Fig. 14. Y

In Fig. 11 a condenser type of microphone is illustrated. The permanentmagnets and pole structure used in conjunction therewith are identicalto that shown in Fig. 12. In this instance a non-magnetic plate 25 isprovided which is stationary and secured to a back panel 26 andinsulated therefrom. The diaphragm 8 is positioned close thereto and isparallel and forms a movable plate or diaphragm of the condenser whilethe plate 25 forms the stationary plate. The plates are connected with asuitable source of current supply with wires 27 and 28. The impact ofthe sound waves causes vibrating movement of the diaphragm 1. This, inturn, transmits movement to the diaphragm 8 and as it moves withrelation to the stationary plate 25, the current fiow through the wires21 and 28 will fluctuate, etc.

In Figs. 7 and 8 a dynamic type of loud speaker l is employed which ismaintained in the magnetic field formed between the pole pieces I 2 3and 4 said pole pieces being connected to the respective legs of thepermanent magnets 5 and (i as shown in Fig. 8. The diaphragm isconnected with a piston 30. Otherwise, the method of suspending thediaphragm is essentially the same as in the other structures. The pistoncarries a small coil 3! (commonly called the voice coil) and this is, inturn, maintained in a magnetic circular air gap 32 formed between thesouth and north pole pieces 33 and 34 which are energized by the arms 33and M through means of the permanent magnets.

When a fluctuating current is introduced in the voice coil the coilWill-generate a flux of its own, which at times enhances the fieldstrength and at other times will weaken same. This will cause the coilto vibrate in unison with the electric fluctuations producing identicalvibrations in the diaphragm, which thus produce sound waves. This typeof apparatus will work equally well as a microphone or a receiver.

From the foregoing it will be noted that in some forms of the apparatustwo diaphragms are desirable While in others one diaphragm will sufficeand that some of the structures may be operated either as microphones orreceivers. Be that as it may, numerous other forms of telephoneapparatus employing the principles'here disclosed could be depictedbut-for the purpose of illustration and description it is thought thatthose already submitted should be sufiicient.

In all of the structures disclosed the diaphragms, whether there be oneor two in number, are maintained in a magnetic field and this field isof sufficient strength to oppose inertia forces and natural periods ofvibrations in the diaphragms. The magnetic fields in which thediaphragms are maintained also function to return the diaphragms to aneutral or inactive position when the force or forces applied theretoare reduced or removed. The magnetic fields, furthermore, provide ameans whereby the movement of the diaphragms laterally of the fields maybe increased or decreased and, furthermore, permits transmission ofmovement from one diaphragm to another at substantially any ratiodesired. The result is a telephone apparatus in which distortion ofsound waves, whether from one source or another, is substantiallyeliminated and in which the diaphragm is so sensitive to sound wavesthat it is able to follow the intricate to and fro motions of the wavesthus insuring fidelity and true sound or tone-like production andtransmission.

While certain features of the present invention have been more or lessspecifically described and illustrated, I wish it understood thatvarious changes may be resorted to Within the scope of the appendedclaims. Similarly, that the materials and finish of the several partsemployed may be such as the manufacturer may decide, or varyingconditions or uses may demand.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:-

1. A method of magnetically counteracting inertia forces and naturalfrequency vibrations in sound translating diaphragms, which consists inbodily suspending the diaphragm in a magnetic field and parallel to themagnetic flux in the field, and securing the diaphragm against bodilymovement longitudinally of the flux but permitting movement transverselythereof.

2. A method of magnetically counteracting inertia forces and naturalfrequency vibrations in sound translating diaphragms, which consists inbodily suspending the diaphragm in a magnetic field and parallel to themagnetic fiux in the field, securing the diaphragm against bodilymovement longitudinally of the fiux but permitting movement transversethereof, and controlling transverse movement of the diaphragm.

3. In a sound translating apparatus having a pair of spaced diaphragms,a method of transmitting motion from one diaphragm to the other, whichconsists in placing the diaphragms in a magnetic field in which the fiuxis parallel to the faces of the diaphragms and maintaining the directionof the fiux so that a magnetic repulsion force is set up between thediaphragms whereby movement imparted to one diaphragm is magneticallytransmitted to the other.

4. In a sound translating apparatus having a pair of spaced diaphragms,a method of transmitting motion from one diaphragm to the other, whichconsists in placing the diaphragms in a magnetic field in which the fluxis parallel to the faces of the diaphragms and maintaining the directionof the fiux so that a magnetic repulsion force is set up between thediaphragms whereby movement imparted to one diaphragm is magneticallytransmitted to the other and concentrating the flux to varying degreeswith relation to the faces of the respective diaphragms to regulate themovement of one diaphragm with relation to the other.

5. A method of controlling movement imparted to sound translatingdiaphragms which consists in bodily suspending the diaphragm in amagnetic field between a plurality of surrounding magnets and parallelto the magnetic flux in the field, and limiting the field transverselyto control bodily movement of the diaphragm transverse to the field.

6. A method of controlling movement imparted to sound. translatingdiaphragms which consists in bodily suspending the diaphragm in amagnetic field between a plurality of surrounding magnets and parallelto the magnetic flux in the field, and limiting the field with relationto the faces of the diaphragm to control bodily movement of thediaphragm transverse to the field.

7. A method of controlling movement imparted to sound translatingdiaphragms which consists in bodily suspending the diaphragm in amagnetic field between a plurality of surrounding magnets and parallelto the magnetic flux in the field, and limiting the field in thedirection of movement of the diaphragm to coritrol bodily movement ofthe diaphragm.

8. A method of magnetically counteracting inertia forces and naturalfrequency vibrations in sound translating diaphragms which consists insurrounding the diaphragm with a plurality of magnetic poles toestablish a magnetic field parallel to the faces of the diaphragm,positioning the poles with alike poles opposing each other so as tomaintain a uniform magnetic field about the diaphragm, and securing thediaphragm against movement longitudinally of the flux but permittingbodily movement transverse thereof.

9. A method of magnetically counteracting inertia forces and naturalfrequency vibrations in sound translating diaphragms which consists insurrounding the diaphragm with a plurality of magnetic poles toestablish a magnetic field parallel to the faces of the diaphragm,positioning the poles with alike poles opposing each other so as tomaintain a uniform magnetic field about the diaphragm securing thediaphragm against movement longitudinally of the fiux but permittingbodily movement transverse thereof, and limiting the width of the fieldto control movement imparted to the diaphragm.-

10. A method of mounting a sound translating diaphragm which consists inplacing a plurality of magnetic poles in'circular formation, with alikepoles opposing each other to establish a uniform magnetic field betweenthe poles, placing a magnetic circular diaphragm centrally in the fieldformed between the poles with an air gap between the peripheral edge ofthe diaphragm and the poles and securing the diaphragm against radialmovement, said securing means permitting bodily movement of thediaphragm at right angles to the field.

11. In a sound translating apparatus of the character described a fiatcircular magnetic diaphragm, a plurality of segment-shaped magneticpoles arranged in circular formation around the diaphragm and spacedtherefrom to form a circular air gap and to form a magnetic field inwhich the flux is parallel to the opposite faces of the diaphragm, andmeans securing the diaphragm against radial movement between themagnets, said means permitting bodily movement of the diaphragm in adirection transverse to the magnets.

12. In a sound translating apparatus of the character described a fiatcircular magnetic diaphragm, a plurality of segment-shaped magneticpoles arranged in circular formation around the diaphragm and spacedtherefrom to form a circular air gap and to form a magnetic field inwhich the flux is parallel to the opposite faces of the diaphragm, and aflexible retaining ring attached to the peripheral edge of the diaphragmand securing it against radial movement with relation to the magneticpoles but permitting free bodily movement of the diaphragm transverse ofthe magnetic field.

13. In a sound translating apparatus of the character described a pairof spaced fiat circular magnetic diaphragms, a plurality of magnetssurrounding the diaphragms, said magnets terminating in poles with alikepoles diametrically opposite each other to form a magnetic field betweenthe poles in which the fiux is parallel to the faces of the diaphragmsand to establish a secondary fiux in the diaphragms which form alikeopposing poles on the diaphragms and thereby produces a repulsion actionbetween the diaphragms, whereby when movement is imparted to onediaphragm said movement will be imparted to the other diaphragm.

14. In a sound translating apparatus of the character described a pairof spaced fiat circular magnetic diaphragms,.a plurality of magnetssurrounding the diaphragms, said magnets terminating in poles with alikepoles diametrically opposite each other to form a magnetic field betweenthe poles in which the flux is parallel to the faces of the diaphragmsand to establish a secondary fiux in the diaphragms which form alikeopposing poles on the diaphragms and thereby produce a repulsion actionbetween the diaphrams, whereby whenmovement is imparted to one diaphragmsaid movement will be imparted to the other diaphragm, and meanssecuring the diaphragms against radial movement in the magnetic fieldbut permitting movement of the diaphragms transverse thereof.

15. In a sound translating apparatus of the character described a pairof spaced fiat circular magnetic diaphragms, a plurality of magnetssurrounding the diaphragms, said magnets terminating in poles with alikepoles diametrically opposite each other to form a magnetic field betweenthe poles in which the fiux is parallel to the faces of the diaphragmsand to establish a secondary flux in the diaphragms whichform alikeoppos- 10 ing poles on the diaphragms and thereby produce a repulsionaction between the diaphragms,

whereby when movement is imparted to one diaphragm, said movement willbe imparted to the other diaphragm, means securing the diaphragmsagainst radial movement in the magnetic field but permitting movement ofthe diaphragms transverse thereof, and means for concentrating themagnetic field to varying degrees with relation to the faces of therespective diaphragms to control movement of the diaphragms transverseof the magnetic fields.

JOHN KALSEY.

